Hybrid storage systems often include storage devices of different types and/or speeds. For example, a hybrid storage system may include one or more high-speed storage devices (such as caches) and/or one or more low-speed storage devices (such as disks) that store data used by various Virtual Machines (VMs) running within a network. In this example, the VMs may initiate various Input/Output (I/O) operations (such as reads and/or writes) serviced by the hybrid storage system.
Delivery of such I/O operations from the VMs to the hybrid storage system may be controlled by a Quality of Service (QoS) feature. For example, a conventional QoS feature may deliver several thousand I/O operations from the VMs to the hybrid storage system every second. In this example, the conventional QoS feature may determine how many I/O operations to deliver to the hybrid storage system by assuming that the high-speed storage devices will service a certain number of I/O operations and the low-speed storage devices will service the remaining I/O operations. Unfortunately, since the conventional QoS feature has no way of knowing exactly which I/O operations will be serviced by the high-speed devices or the low-speed devices at the time of arrival, the conventional QoS feature's assumption about the number of I/O operations serviced by the high-speed storage devices as opposed to the low-speed storage devices may be incorrect and/or lead to latency problems within the hybrid storage system.
As an example, the conventional QoS feature may deliver I/O operations from the VMs to the hybrid storage system at a certain rate. In the event that many, if not all, of these I/O operations are serviced by the high-speed storage devices, the hybrid storage system may demonstrate a period of very low latency, thereby potentially giving the conventional QoS feature a false impression that the hybrid storage system is able to service such I/O operations at even higher speeds. As a result, the conventional QoS feature may increase the rate of delivery for the I/O operations such that some of the I/O operations quickly fill up the storage space within the high-speed storage devices and the remaining I/O operations are forced to skip to the low-speed storage devices, thereby potentially leading to a period of very high latency. These back-and-forth changes in latency may cause the conventional QoS feature to repeatedly and/or unstably flip-flop the delivery rates for the I/O operations.
The instant disclosure, therefore, identifies and addresses a need for systems and methods for improving QoS within hybrid storage systems.